[c-nsp] Label still appearing in traceroute after disabling ttl propagation

[John Neiberger]

After a little more investigation, I think the problem is that our P2
router is not learning a set of prefixes via LDP that it should be, so it
is sending them unlabeled to PE2. We assumed that both P routers had the
right labels, but that doesn't appear to be the case.


On Tue, Jul 30, 2013 at 12:20 PM, John Neiberger <jneiberger at gmail.com>wrote:

> I guess I should rephrase. We have configured "mpls ip-ttl-propagate
> disable" to try to hide the labeled part of the path. For whatever reason,
> we always get something like the following:
> CE1#trace 10.6.10.1 source lo0
> Type escape sequence to abort.
> Tracing the route to 10.6.10.1
> VRF info: (vrf in name/id, vrf out name/id)
>   1 192.168.105.50 0 msec 0 msec 0 msec
>   2 192.168.62.2 [MPLS: Label 16018 Exp 0] 4 msec 0 msec 0 msec
>   3 192.168.62.60 0 msec 0 msec 0 msec
>   4 192.168.106.61 4 msec *  0 msec
> CE1#
> If I trace from CE1 to the loopback of PE2, which is the same path, it
> works as expected and the labeled part of the path is hidden:
>
> CE5#trace 10.6.1.1 source lo0
> Type escape sequence to abort.
> Tracing the route to 10.6.1.1
> VRF info: (vrf in name/id, vrf out name/id)
>   1 192.168.105.50 4 msec 0 msec 0 msec
>   2 192.168.62.60 0 msec *  0 msec
>
>
> On Tue, Jul 30, 2013 at 11:43 AM, Jared Mauch <jared at puck.nether.net>wrote:
>
>> Disable TTL != don't copy label into ICMP TTL Expired message.
>>
>> - Jared
>>
>> On Jul 30, 2013, at 1:37 PM, John Neiberger <jneiberger at gmail.com> wrote:
>>
>> > I think either we're just doing something wrong or perhaps we're running
>> > into a bug. I did find this one, which sounds similar:
>> >
>> > https://tools.cisco.com/bugsearch/bug/CSCtd17126
>> >
>> > I'm not sure if that is fixed in 4.1.0 or not.
>> >
>> >
>> > On Tue, Jul 30, 2013 at 11:01 AM, John Neiberger <jneiberger at gmail.com
>> >wrote:
>> >
>> >> W
>> >> e're running into an interesting problem. We have a simple lab setup
>> like
>> >> this:
>> >>
>> >> CE1 -- PE1 --- P1 --- P2 --- PE2 --- CE2
>> >>
>> >> We have "mpls ip-ttl-propagate disable" on all PE and P routers, but
>> if we
>> >> trace from CE1 to CE2, we still see an MPLS label coming from the PE2
>> >> router. If we trace CE2 to CE1, we see a label on the hop from P1 to
>> PE1.
>> >>
>> >> If we have ttl propagation completely disabled, why would we still see
>> the
>> >> label and P-to-PE link in the path?
>> >>
>> >> All P and PE routers are IOS XR running 4.1.0.
>> >>
>> >> Thanks,
>> >> John
>> >>
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>>
>